Examination of metals and alloys

Objects of metallurgical expertise are seized in almost all categories of criminal and civil cases and can be objects of research not only for this kind of expertise, but also for complex metallurgical, other classes and types of expertise: trasological, electrical, fire-technical, ballistic, explosive, autotechnical. Metallurgical expertise is in demand by the customs authorities for foreign trade operations. / P>

The most common diagnostic questions are:

• what metal, alloy this item is made of (fragment);
• what is the brand of this metal, alloy; what is the scope of this metal, alloy;
• whether there is a metal coating on the presented object;
• what are its composition and purpose; whether there are metal particles on the carrier object; what is their composition; for the manufacture of what household products this metal could be intended;
• whether there are traces of metallization on the carrier object and what composition; what is the source of their origin; the object of what shape and size they could be left;
• whether the metal (alloy) presented for research is precious; what is the percentage of components in it and what sample does it correspond to; whether this gold is native or industrial; whether this piece of jewelry is made of native or industrial gold; from which deposit this native gold originates;
• what is the method of manufacturing this product; what processing it was subjected to; how long the object was oxidized (rusty); what are the causes and mechanism of destruction of this metal object (node, part);
• whether a metal coin or medal is counterfeit; what alloy of them and in what way (for example, casting into a non-metallic or metallic form, stamping using a matrix and a punch made by engraving, etc.) it was made;
• whether there are traces of melting on the presented metal objects; whether the melting of cable products (electrical wires and cables), metal pipes and metal hoses, electrical panel housings and other products occurred as a result of external thermal effects or emergency operation of the power grid; if reflow occurred due to emergency mode, then under what conditions (for example, before the fire: room temperature and the absence of combustion products in the air, or during the development of a fire: in conditions of high temperature and smoke);
• how is this metal object divided into parts; whether a thermal cutting device was used for this, the type of this device; what welding consumables were used for cutting; what was the qualification of the person who performed the electric arc (oxy-fuel) cutting.

Identification issues within the framework of the metallurgical expertise include:

• whether the metal or alloy from which the products and comparative samples are made (for example, a ring and an ingot of gold) have a common group affiliation in composition;
• whether a metal product (fragment) and comparative samples have a common group affiliation in terms of manufacturing and operation features;
• whether this object and comparative samples were made from the same alloy, steel grade;
• whether this metal fragment is part of this product (a metal particle removed from the victim's body and a knife, a plate with a number and a car body, etc.);
• whether this object is made from a specific metal object (a knife blade from a given steel plate, a crown from discovered industrial gold);
• whether the compared metal objects belong to a single source of origin: to the products of one plant (for example, sheets of roofing iron), a single batch, a single mass (native gold and gold particles on a microbalance);
• at the same or different deposits, gold was mined, seized from several suspects (or is this native gold mined at a certain deposit, is this jewelry made of gold from a certain deposit).

Microparticles of metals and alloys and traces of metallization (in combination with other objects) can be used to establish the fact of contact interaction of objects.

For example, when conducting a metallurgical examination of fused wires, the metallurgical examination establishes the conditions for the formation of metal fusion; in combination with the electrical one - issues related to the causes of emergency operation of the power grid are resolved, and in combination with the fire-technical one - the presence of a cause-and-effect relationship in the emergency mode in the power grid, conductor melting and fire

As part of the metallurgical expertise, small permanent magnets are used to detect microparticles of ferrous metals. Microparticles of metals and alloys and traces of metallization are removed together with the carrier object. Fragments of electrical wiring containing reflow are marked, the places of their removal are indicated on the electrical diagram of the object and its plan.

To carry out a metallurgical examination, metal objects are each packed separately in paper bags or cardboard boxes and supplied with explanatory notes. If there are foreign deposits on them, for example, blood, or objects are damp (the knife is removed from the reservoir), they must be dried at room temperature before packing. Sealed packaging of wet metal objects or objects with biological layers, for example, in plastic wrap, is highly undesirable, since metal corrosion and decomposition (decay) of layers may begin.